Kim Jong-un, the leader of North Korea, in April. North Korea stands accused of assassinating his estranged half brother, Kim Jong-nam, in May.

SEOUL, South Korea — In a region already tense over nuclear threats, North Korea accused the South Korean and American intelligence agencies on Friday of plotting to assassinate its leader, Kim Jong-un, and it warned of an unspecified counterattack. The North Korean government said it had recently uncovered a “hideous terrorists’ group” that the South Koreans and the C.I.A. had sent into the country on a secret mission to kill Mr. Kim with biochemical agents. A statement carried by the country’s official news agency, KCNA, said that South Korea’s National Intelligence Service had hired a North Korean logger working in the Russian Far East in 2014 to attack Mr. Kim. The existence of such a plot is impossible to verify. The National Intelligence Service dismissed the accusations as groundless. North Korea is especially sensitive to any hint of criticism or threat to its leader. Even a movie version of such a threat roiled the country. North Korea is widely believed to have mounted an audacious hacking attack of Sony Pictures in 2014 as retaliation against “The Interview,” a comedy based on a fictional plot to assassinate Mr. Kim. And when North Korea executed Mr. Kim’s uncle, Jang Song-thaek, it accused him of plotting to overthrow Mr. Kim’s government. The fears run so high that when Mr. Kim — and, before him, his father, the dictator Kim Jong-il — was scheduled to appear in public, agents removed residents from nearby apartments, according to defectors who had served in North Korean security agencies. Even soldiers who were designated to shake hands with Mr. Kim had to wash their hands first, the defectors said. The country’s relationship with South Korea and the United States has been particularly tense in recent months, as the North threatened to perform another nuclear test and continued to test ballistic missiles. President Trump has rattled the region with martial-sounding threats, including a recent comment that the United States could “end up having a major, major conflict with North Korea.” On Monday, however, Mr. Trump said he was willing to meet with Mr. Kim if the circumstances were right, a departure from past sitting presidents who have shunned the North Korean leadership. The North Korean government laid out its claims of a plot against Mr. Kim in surprising detail on Friday. It said that officers at South Korea’s National Intelligence Service had trained the man in the assassination plot, and provided him with $20,000 and a satellite communication device. His handlers then sent the “human scum” into North Korea, giving him instructions last year on how to assassinate Mr. Kim, according to a spokesman for the North’s Ministry of State Security. The ministry serves as the North’s intelligence and secret police agency. The plan involved bombing a military parade attended by Mr. Kim, the North Korean statement said. The South Korean spy agency later provided the man with additional cash to hire co-conspirators, the statement said. The statement then threatened that an “anti-terrorist attack will be commenced from this moment to sweep away the intelligence and plot-breeding organizations of the U.S. imperialists and the puppet clique, the most mean and brutal hideous terrorist group in the world.” In North Korean propaganda, South Korea is regularly referred to as a puppet of the United States. In recent years, at least three South Koreans have been arrested in North Korea and sentenced to long prison terms on espionage charges. The North is also holding at least three Americans on charges of “hostile acts,” including a Korean-American named Kim Dong-chul, whom it accused of spying for the South. It remains impossible to verify these claims. South Korea’s National Intelligence Service dismisses them as propaganda. North Korea has also made improbable allegations that more than 30,000 North Korean defectors who fled to South Korea in the last two decades were kidnapped by the South. When it accused the South Korean spy agency in these cases, it usually named the C.I.A. as either a co-conspirator or the mastermind. Still, it is highly unusual for North Korea to assert that the South’s spy agency plotted to assassinate Mr. Kim. In recent months, as tensions intensified on the Korean Peninsula, the North has reacted stridently to news reports out of South Korea that United States and South Korean commando units were training to “decapitate” the North Korean leadership in case of war. Over the decades, there have been occasional, unconfirmed reports of armed rebellions or assassination attempts in the North. But longtime North Korea observers say that organized subversion is highly unlikely under the North’s police state, in which huge numbers of soldiers and security agents are dedicated to the sole task of protecting Mr. Kim. In 2004, an enormous explosion at a train station on the border with China prompted rumors of an attempt to kill Kim Jong-il, who had passed through nine hours earlier on his way back from Beijing. Two trains carrying fuel had collided, killing or injuring as many as 3,000 people, but no connection to the leader’s travel was ever confirmed. In the fraught history of the Korean Peninsula, however, the idea of assassination attempts is not far-fetched. In 1968, North Korean commandos came within striking distance of the South Korean president’s home, the Blue House, before being repelled. One agent caught alive said his team had snaked through the border to “slit the throat” of the South Korean leader at the time, Park Chung-hee. In retaliation, Mr. Park’s government trained a secret unit with a mission to assassinate his nemesis, Kim Il-sung, Mr. Kim’s grandfather. The unit was disbanded without carrying out its mission. In 1983, North Korea tried to assassinate another South Korean dictator, Chun Doo-hwan, while he was visiting Burma, now Myanmar. The bombs planted by its officers destroyed the Martyrs’ Mausoleum in what was then the Burmese capital, killing 21 people, including several South Korean cabinet ministers. Mr. Chun escaped the attack because his arrival had been delayed. The latest allegations follow the assassination of Kim Jong-nam, Mr. Kim’s estranged half brother, with a banned chemical weapon at Kuala Lumpur International Airport in February. That killing has been linked to North Korea. Reported By: Parminder Singh #DCPBVM